Just a quickie, if you want to edit the curves of an animated parameter and own another 3D app that has a means of exporting an animation to a .chan file (in my case XSI, so I've no idea what's out there for other apps):
I like to use Johnnyboy's xsi2chan jscript. It's straightforward and no hassle; just remember to change the scaling from 10 to 1 when the output dialog pops up.
http://forums.planetside.co.uk/index.php?topic=246.msg1815#msg1815 (after downloading, change the suffix from .txt to .js)
In Terragen, do your setup and note what you like in terms of the parameters settings.Go to XSI and create a new camera.
Un-parent the Camera from the Camera Root, and delete the Camera Root which is not needed for this.
Animate the camera's X translation to the values you want in Terragen, and edit the animation curve.
Load xsi2chan in the XSI script editor, select the camera and run the script. Change the scaling to 1, and export the .chan file.In Terragen, go to the animated parameter, click on the Animation button and Import the .chan file you just made.That's it.
The .chan file import for a single parameter in Terragen will load the first column from the .chan file, which is the X translation. I'm sure this could be adapted for use with any 3D app, or even 2D app, if a .chan export option is there.